The present invention relates to a load control device for an engine of a work vehicle.
A wheel loader travels by an engine that drives drive wheels (traveling wheels) via a torque converter as a drive source. The engine also functions as a drive source for a steering mechanism and a work machine such as a loader. Specifically, a steering hydraulic pump is driven by the engine, and pressure oil discharged from the steering hydraulic pump is supplied to a steering hydraulic cylinder, whereby the steering mechanism is operated. Also, a loader hydraulic pump is driven by the engine and pressure oil discharged from the loader hydraulic pump is supplied to a loader hydraulic cylinder, whereby the loader is operated. The steering hydraulic pump and the loader hydraulic pump are provided with a fixed displacement hydraulic pump having a fixed displacement.
The traveling speed of the wheel loader varies according to a depressing amount of an accelerator pedal. This means that the engine speed is varied according to the depressing amount of the accelerator pedal, and the vehicle speed is varied according to the change in the engine speed. The target engine speed varies in a range from a low idling speed to a high idling speed.
The vehicle speed becomes zero by releasing the accelerator pedal to the non-depressed state, and the work is done in the halted state.
Thus, the wheel loader is operated more often with the target engine speed set to a low idling speed (idling mode) in comparison with other work vehicles such as a hydraulic excavator.
On the other hand, the engine has characteristics that the engine torque increases more slowly in response to a rapid increase of the hydraulic load when the engine speed is in a low speed range, or at a low idling speed than when in a high speed range, or at a high idling speed.